The disclosure of Japanese Patent Application No. 2001-290574 filed on Sep. 25, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention generally relates to vibration-damping devices for use in various kinds of vibrative members, for reducing or attenuating vibrations excited in these vibrative members. More particularly, the present invention is concerned with such a vibration-damping device, which is novel in construction and which is suitably used in an automotive vehicle for damping or attenuating vibrations excited in a suspension member, a sub frame, a body, a mounting bracket, a vibrative member or members used in an engine unit or an exhaustion system, and other vibrative members.
2. Description of the Related Art
Vibration-damping devices have been used in various kinds of vibrative members for damping vibrations excited therein. Known examples of these vibration-damping devices include (a) a mass damper in which a pillar-shaped mass member is fixed to a vibrative member; (b) a dynamic damper in which a pillar-shaped mass member is supported by and connected to the vibrative member via a spring member; and (c) a damping material which is a sheet-shaped elastic member and secured to the vibrative member. However, these conventional devices suffer from various potential problems. For instance, the mass damper and the dynamic damper require a relatively large weight of the pillar-shaped mass member, and exhibit damping effects limited to a considerably narrow frequency range. The damping material requires a relatively large space for its installation, and tends to be large in its weight. In addition, the dynamic damper and the damping material both suffer from difficulty in stably exhibiting desired damping effects thereof, since the damping effects of the dynamic damper and the damping material are prone to vary depending upon the ambient temperature.
The present assignee has been disclosed in International Publication No. WO 00/14429 a novel vibration damper for use in an automotive vehicle, which includes a housing member having an inner space and fixed to the vibrative member, and an independent mass member which is disposed within the inner space of the housing member with a spacing therebetween, without being bonded to the housing member, so that the independent mass member is displaceable or movable relative to the housing member. When vibrations excited in the vibrative member is applied to the vibration damper, the independent mass member and the housing member are brought into elastic impact against each other at their abutting surfaces, thereby exhibiting a vibration damping effect on the basis of loss or dissipation of vibration energy caused by sliding friction generated between the elastic abutting surfaces of the independent mass member and the housing member and caused by collision or impact of the independent mass member on the housing member. This proposed vibration damper is capable of exhibiting a high damping effect over a relatively wide frequency range of input vibrations, while assuring a relatively small weight or mass of the independent mass member.
Extensive studies of the vibration damper disclosed in the International Publication No. WO 00/14429, conducted by the inventors of the present invention, have revealed that the disclosed vibration damper can exhibit such a high damping effect based on a bouncing or jumpily displacement of the mass member relative to the housing member in which the mass member comes into impact on and rebounds from the housing member repeatedly. In order to upgrade the damping effect of the disclosed vibration damper with respect to vibrations excited in the automotive vehicle, namely, vibrations having a relatively low frequency, a relatively small amplitude and a relatively small energy, it is therefore effective to sufficiently decrease a spring stiffness of an elastic body at least partially defining the abutting portion of the mass member, which is adapted to be brought into abutting contact with the housing member, thereby facilitating the jumpily displacement of the mass member relative to the housing member.
To obtain a sufficiently small spring stiffness of the elastic body at least partially defining the abutting portion of the mass member, it may be proposed to arrange the elastic body of the mass member to have a relatively large wall thickness enough to establish a sufficiently small dynamic spring constant of the abutting surface of the mass member, or alternatively, to form the elastic body of the mass member of a soft rubber material. However, in the former case, the wall thickness of the elastic body is likely to be limited by a size of a space for housing the mass member, and in the latter case, the elastic body is likely to be deteriorated in terms of its durability. Therefore, the disclosed vibration damper is less likely to excite the jumpily displacement of the mass member relative to the housing member upon application of such vibrations having the small energy, low frequency and small amplitude, thereby suffering from difficulty in exhibiting a desired vibration damping effect with respect to such vibrations. Thus, the disclosed vibration damper leaves some room for improvement.
It is therefore one object of this invention to provide an improved vibration-damping device, which makes it possible to reduce a dynamic spring constant at an abutting portion of a mass member with respect to a housing member, without needing an increase of a wall thickness of an elastic body at least partially defining the abutting portion of the mass member and/or the housing member, and without causing deterioration of durability of the elastic body due to a change of a rubber material for forming the elastic body. Therefore, the vibration-damping device is capable of efficiently exciting jumpily displacement of the mass member relative to the housing member, even upon application of vibrations having a small energy, a low frequency and a small amplitude to the vibration-damping device, and accordingly exhibiting an excellent vibration damping effect based on impact of the mass member on the housing member, for these vibrations having the small energy, low frequency and small amplitude.
The above and/or optional objects of this invention may be attained according to at least one of the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depending from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to these modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety.
(1) A vibration-damping device for damping vibrations excited in a vibrative member, comprising: (a) a housing member adapted to be fixed to the vibrative member and defining a accommodation space therein; (b) a pillar-shaped mass member housed within the accommodation space of the housing member with a slight spacing therebetween so that the pillar-shaped mass member is independent of the housing member and is freely displaceable within the accommodation space of the housing member to come into impact on the housing member, the pillar-shaped mass member extending in a primary vibration input direction; and (c) a rubber buffer and an abutting rubber member, which are integrally formed with each other and fixed to at least one of axially opposite end portions of the pillar-shaped mass member such that the rubber buffer covers an outer circumferential surface of the at least one of axially opposite end portions of the pillar-shaped mass member, and the abutting rubber member extends axially outwardly from the rubber buffer so that the abutting rubber member is disposed over an end face of the at least one of axially opposite end portions of the pillar-shaped mass member, and the pillar-shaped mass member comes into impact at a protruding end portion of the abutting rubber member on the housing member, wherein a void is formed between the abutting rubber member and the at least one of axially opposite end portions of the pillar-shaped mass member so that the abutting rubber member undergoes shear deformation upon impact of the pillar-shaped mass member on the housing member at the protruding end portion of the abutting rubber member.
According to this mode of the invention, when the pillar-shaped mass member comes into impact on the housing member via the abutting rubber member in the vibration input direction, the abutting rubber member, which defines an abutting portion of the pillar-shaped mass member with respect to the housing member, undergoes shear deformation. This arrangement makes it possible to reduce or minimize a dynamic spring constant of the abutting portion of the pillar-shaped mass member with respect to the housing member, without needing a significant increase of a wall thickness of the abutting rubber member, or a change of a rubber material for forming the abutting rubber member, which may be required in the case where the rubber abutting member undergoes compression deformation, in order to reduce the dynamic spring constant of the abutting portion of the pillar-shaped mass member. Thus, the vibration-damping device according to this mode of the invention is capable of effectively exciting a bouncing or jumpily displacement of the pillar-shaped mass member relative to the housing member when the vibration-damping device is subjected to vibrations to be damped.
Therefore, the vibration-damping device of this mode of the invention can facilitate the bouncing displacement of the pillar-shaped mass member relative to the housing member, upon application of a vibration having a relatively small energy. For instance, even if an acceleration of the input vibration is not larger than 1 G (a gravity acceleration), the vibration-damping device of this mode of the invention enables the pillar-shaped mass member to bounce off the housing member by reducing the dynamic spring constant of the abutting rubber member, thereby assuring a bouncing displacement of the pillar-shaped mass member relative to the housing member. Thus, the vibration-damping device of this mode of the invention can exhibit a desired damping effect based on the impact (or the abutting contact) of the pillar-shaped mass member on the housing member with respect to the vibrations having a relatively small energy, as well.
According to this mode of the invention, more over, the abutting portion of the pillar-shaped mass member with respect to the housing member is fixedly set to the protruding end portion of the abutting rubber member. This makes it possible to stabilize a position at which the pillar-shaped mass member and the housing member are brought into impact against each other, relative to a center of gravity of the pillar-shaped mass member, even if the pillar-shaped mass member is displaced relative to the housing member in a radial direction perpendicular to an axial direction of the pillar-shaped mass member when performing the bouncing displacement. Therefore, this arrangement allows the vibration-damping device to exhibit the above-mentioned desired damping effect based on the impact of the pillar-shaped mass member on the housing member with high stability.
Preferably, the housing member is formed of iron or other metallic materials having a sufficiently high rigidity so that the vibration damping effect as a result of impact of the pillar-shaped mass member on the housing member is effectively transmitted to the vibrative member. On the other hand, the pillar-shaped mass member is preferably formed of a high gravity material such as iron so as to have a desired mass or weight with a relatively small volume. The shape of the accommodation space defined within the housing member may be desirably determined with a size and a shape of the pillar-shaped mass member taken into consideration, so as to permit a free displacement of the pillar-shaped mass member in the vibration input direction, while limiting undesirable or unnecessary displacement of the pillar-shaped mass member, e.g., a slant or a side travel or slip.
The pillar-shaped mass member may have a variety configurations so long as at least one of axially opposite end portions of the pillar-shaped mass member is provided with the abutting rubber member so as to form the abutting portion of the pillar-shaped mass member with respect to the housing member. For instance, a solid cylindrical member having a circular or polygonal shape in its transverse cross section may be preferably employed as the pillar-shaped mass member. Preferably, the pillar-shaped mass member comes into impact on the housing member at both of axially opposite sides thereof, thereby exhibiting a desired damping effect with further improved efficiency. If the vibration input direction extends in the vertical direction, the abutting portion may be provided only for an axially lower end portion of the pillar-shaped mass member.
The rubber buffer may be desirably formed so long as it is formed on an outer circumferential surface of at least one of axially opposite end portions of the pillar-shaped mass member. For instance, the rubber buffer may be formed on the entire area of the outer circumferential surface of the pillar-shaped mass member, or alternatively may include a lip-shaped projection integrally formed on and protruding from the outer circumferential surface of the rubber buffer, which extends in a desired direction, e.g., the circumferential direction or the axial direction. When the rubber buffer is formed on the outer circumferential surface of the at least one of axially opposite end portions of the pillar-shaped mass member, the outer diameter of the at least one of axially opposite end portions of the pillar-shaped mass member is made smaller by a given radial dimension for permitting the rubber buffer to have a desired wall thickness, while avoiding enlargement of the outer diameter of the pillar-shaped mass member, thereby providing the vibration-damping device which is made compact in size.
The rubber buffer and the abutting rubber member may be formed by vulcanizing a suitable rubber material in a mold cavity designed for forming the rubber buffer and the abutting rubber member, wherein the pillar-shaped mass member is disposed in position, so that the rubber buffer and the abutting rubber member are bonded to the pillar-shaped mass member at the time of the vulcanization of the rubber material, thereby providing an integrally vulcanized product consisting of the pillar-shaped mass member, the rubber buffer and the abutting rubber member. Alternatively, the rubber buffer and the abutting rubber member may be formed independent of the pillar-shaped mass member in advance, and then are fixed to the pillar-shaped mass member.
(2) A vibration-damping device according to the above indicated mode (1), wherein the rubber buffer and the abutting rubber member are integrally formed with each other to form an end rubber member, which is independent of the pillar-shaped mass member, and is firmly assembled by press fitting onto the at least one of axially opposite end portions of the pillar-shaped mass member. According to this mode of the invention, a cumbersome adhesive treatment is no longer needed upon forming the rubber buffer and the abutting rubber member. This simplifies the process of manufacturing the vibration-damping device, and makes it possible to form the void located between the abutting rubber member and the at least one of axially opposite end portions of the pillar-shaped mass member with ease in a desirable form. This arrangement also provides the vibration-damping device with an option to tune its damping characteristics by suitably selecting a combination of the pillar-shaped mass member and the end rubber member from among pillar-shaped mass members having different masses and end rubber members having different spring characteristics.
(3) A vibration-damping device according to the above indicated mode (1) or (2), wherein a principal elastic axis of the abutting rubber member is arranged to extend through a center of gravity of the pillar-shaped mass member, and the abutting rubber member has an abutting surface to be brought into abutting contact with the housing member, which is defined by a plane extending in a direction perpendicular to the principal elastic axis of the abutting rubber member. The vibration-damping device according to this mode of the invention is able to stabilize the elastic deformation of the abutting rubber member upon impact of the pillar-shaped mass member on the housing member, thereby stabilizing the jumpily displacement of the pillar-shaped mass member and a resultant damping effect. It should be appreciated that the abutting surface may be formed as a single form, or alternatively may be divided into a plurality of segments.
(4) A vibration-damping device according to any one of the above-indicated modes (1)-(3), wherein the housing member includes a plane surface which is opposed to the abutting rubber member, and which extends in a radial direction perpendicular to a central axis of the pillar-shaped mass member over an area larger than an abutting area to which the abutting rubber member is brought into abutting contact with the housing member. According to this mode of the invention, even if the pillar-shaped mass member shifts its position in the horizontal direction on the plane surface during its jumpily displacement, the pillar-shaped mass member can be brought into impact on the housing member with the substantially same abutting condition, making it possible to stabilize the damping effect of the vibration-damping device based on the impact of the pillar-shaped mass member on the housing member.
(5) A vibration-damping device according to any one of the above-indicated modes (1)-(4), wherein the abutting rubber member is formed with a through hole through which the void is exposed to the accommodation space. This arrangement can avoid that the closed void functions as an air spring when the abutting rubber member is elastically deformed, further effectively assuring the low dynamic spring constant of the abutting rubber member, while stabilizing the spring characteristics of the abutting rubber member and the damping effect of the vibration-damping device based on the jumpily displacement of the pillar-shaped mass member.
(6) A vibration-damping device according to any one of the above-indicated modes (1)-(5), further comprising a cushioning projection formed at a portion of an inner surface of the abutting rubber member defining the void, so as to be opposed to and protrude toward the pillar-shaped mass member, in a direction of a central axis of the pillar-shaped mass member. The cushioning projection functions to absorb or attenuate impact or noises when an excessively large vibration energy acts on the abutting rubber member, and whereby the abutting rubber member is brought into abutting contact with the pillar-shaped mass member due to a large elastic deformation of the elastic support member and the abutting rubber buffer enough to vanish the void.
(7) A vibration-damping device according to any one of the above-indicated modes (1)-(6), wherein the abutting rubber member is formed by using a mold whose parting line is arranged to be spaced away from a molding surface for forming an abutting surface to be brought into abutting contact with the housing member. While a surface or a dimensional accuracy of the abutting surface is an important factor to stabilize the damping effect of the vibration-damping device, this arrangement makes it possible to ensure a high surface or dimensional accuracy of the abutting surface with ease, without needing additional treatment e.g., an elimination of burrs. In order to arrange the parting line of the mold to be spaced away from the molding surface of the abutting surface of the abutting rubber member, at least the protruding end portion of the abutting rubber member may be formed by using a generally cup shaped mold consisting of mold halves moved to each other in the axial direction of the abutting rubber member to close the mold.
(8) A vibration-damping device according to any one of the above-indicated modes (1)-(7), wherein the accommodation space defined within the housing member is fluid-tightly closed from an external area. This arrangement can avoid undesirable entrance of the dust or other foreign substances into the accommodation space defined by the housing, thereby effectively preventing deterioration or insecurity of the vibration damping effects. Thus, the vibration-damping device can assure an improved reliability and stability in its damping capability.
(9) A vibration-damping device according to any one of the above-indicated modes (1)-(8), wherein the abutting rubber member includes: a block-shaped abutting part disposed in a coaxial relationship with the pillar-shaped mass member and located axially outward of the at least one of axially opposite end portions of the pillar-shaped mass member with a spacing therebetween, the block-shaped abutting part being brought into abutting contact with the housing member at an abutting surface thereof, which is smaller than the end face of the at least one of axially opposite end portions of the pillar-shaped mass member; and an elastic support part extending axially outwardly and radially outwardly from an outer peripheral portion of the abutting part toward an outer peripheral portion of the at least one of axially opposite end portions of the pillar-shaped mass member so as to elastically connect the abutting part to the pillar-shaped mass member, such that a principal elastic axis of the elastic support part extends along with a central axis of the pillar-shaped mass member, and the elastic support part is subjected to shear deformation upon impact of pillar-shaped mass member on the housing member at the abutting surface of the abutting part of the abutting rubber member. This vibration-damping device according to this mode of the invention effectively permits the abutting rubber member to come into abutting contact with the housing member with a stable condition, while ensuring a low dynamic spring constant of the abutting rubber member as a result of the shear deformation of the elastic support part. Further, the vibration-damping device according to this mode of the invention ensures the shear deformation of the abutting rubber member when coming into abutting contact with the housing member, while providing the plane surface extending in the radial direction on the axially opposite end faces of the pillar-shaped mass member. Therefore, the use of the pillar-shaped mass member whose axially opposite end faces are made plane makes it facilitate further the manufacture of the desired vibration-damping device of the invention.
Preferably, the block-shaped abutting part has a solid cylindrical block shape with a diameter sufficiently smaller than that of the pillar-shaped mass member, while being disposed in a coaxial relationship with the pillar-shaped mass member. This arrangement enables the abutting rubber member to come into abutting contact with the housing member under a further stabilized condition. Preferably, the elastic support part is formed in a tapered shape extending radially outwardly and axially outwardly from the abutting part to the outer peripheral portion of the pillar-shaped mass member. Alternatively, the elastic support part consists of a plurality of rib-shaped support members, which are substantially spaced away from each other in a circumferential direction, and which extend straightly with a given gradient from the abutting part to the outer peripheral portion of the pillar-shaped mass member. Also, one of axially opposite end portions of the elastic support part, which is located on the side of the pillar-shaped mass member, is superposed on and assembled with an outer peripheral portion of the end face of the at least one of axially opposite end portion of the pillar-shaped mass member, preferably. This arrangement may stabilize the elastic deformation of the elastic support part against a load applied thereto in a direction in which the principal elastic axis of the abutting part extends, resulting in an improved anti-load capability of the elastic support part of the abutting rubber member.
The vibration-damping device constructed according to any one of the above-indicated modes (1)-(9), may be installed on the vibrative member, according to a variety of arrangements. For example, the vibration-damping device of the invention may be installed on the vibrative member such that the housing member is fixedly mounted on the vibrative member so that vibrations excited in the vibrative member is directly applied to the housing member. Alternatively, the vibration-damping device may be installed on the vibrative member such that the housing member is mounted on the vibrative member via a suitable spring member so that the vibrations excited in the vibrative member is indirectly applied to the housing member via the spring member. In the former case, the housing member can be directly fixed to the vibrative member with ease. With the housing member fixed to the vibrative member, active damping effect based on the impact of the pillar-shaped mass member on the housing member can directly affect on the vibrative member. In the latter case, on the other hand, the vibration-damping device mounted on the vibrative member via the spring member constitutes a secondary vibration system for the vibrative member as a primary vibration system. Namely, the pillar-shaped mass member and the housing member cooperate to function as a mass system, while the spring member functions as a spring system in the secondary vibration system. That is, the vibration-damping device installed on the vibrative member via the spring member functions as a dynamic damper, as well. In the latter case, particularly, the vibration-damping device itself functions as the mass system in the secondary vibration system or the dynamic damper, so that a suitable tuning of a natural frequency of the secondary vibration system for a frequency range of vibrations to be damped permits an efficient transmission of the vibrations excited in the vibrative member to the vibration-damping device, thereby actively exciting jumpily displacement of the pillar-shaped mass member within the housing member. Thus, the vibration-damping device mounted on the vibrative member via the spring member can effectively exhibit an excellent damping effect with respect to the vibrations excited in the vibrative member, even if the excited vibrations have relatively small vibration energy.
In the vibration-damping device constructed according to any one of the above-indicated modes (1)-(9), the pillar-shaped mass member is preferably arranged to have a mass within a range of 10-1000 g, more preferably 50-500 g. Namely, the pillar-shaped mass member having the mass of 1000 g or smaller, more preferably 500 g or smaller, is likely to be displaced upon application of vibrational loads to the housing member, making it possible to excite the jumpily displacement of the pillar-shaped mass member more easily and efficiently. Also, the pillar-shaped mass member having the mass of 10 g or larger more preferably 50 g or larger, ensures the vibration-damping device to exhibit an excellent damping effect based on the impact of the pillar-shaped mass member on the housing member.
The vibration-damping device according to any one of the above-indicated modes (1)-(9), may preferably be modified such that the rubber buffer covering the outer circumferential surface of the pillar-shaped mass member is opposed to an inner surface of the housing member in a diametrically opposite sides thereof with a spacing therebetween so that the pillar-shaped mass member is able to travel by a distance of 0.1-1.6 mm, more preferably 0.1-1.0 mm, in a diametric direction. This arrangement makes it possible to minimize an amount of inclination or tilt of the central axis of the pillar-shaped mass member during its jumpily displacement, thus further stabilizing condition upon impact of the pillar-shaped mass member on the housing member.
Preferably, the pillar-shaped mass member is brought into impact at its both sides, which are opposed to each other in the vibration input direction, on respective abutting surfaces of the housing member which are opposed to each other with the pillar-shaped mass member interposed therebetween in the vibration input direction. In particular, a travel distance of the pillar-shaped mass member between the abutting surfaces of the housing member is determined within a range of 0.1-1.6 mm, more preferably 0.1-1.0 mm. Since the gap distance between the pillar-shaped mass member and the housing member is held within the above-described slight dimension, the pillar-shaped mass member is more likely to come into impact on the housing member at its opposite sides in the vibration input direction, even if input vibrations has a relatively small amplitude like vibrations excited in an automotive vehicle, whereby the vibration-damping device of the invention can exhibit an excellent damping effect with respect to the vibrations excited in the automotive vehicle. Particularly, it is very important to make sure the impact of the pillar-shaped mass member on the housing member on the opposite sides of the pillar-shaped mass member in the vibration input direction for ensuring the jumpily displacement of the pillar-shaped mass member, when the vibration-damping device is subjected to vibrations primarily applied thereto in the horizontal direction.
In order to reduce impact noises upon impact of the pillar-shaped mass member on the housing member, the abutting rubber member forming the abutting portion of the pillar-shaped mass member with respect to the housing member, may preferably have a Shore D hardness of 80 or lower, more preferably, within a range of 20-40, as measured in accordance with ASTM method D-2240, while having a modulus of elasticity within a range of 1-104 MPa, more preferably, 1-103 MPa, and a loss tangent is not less than 10xe2x88x923, more preferably within a range of 0.01-10.
Preferably, the vibration-damping device according to the present invention may be modified such that a total mass of the pillar-shaped mass member is held within a range of 5-15%, more preferably 5-10% of a mass of the vibrative member. Namely, if the mass of the pillar-shaped mass member is made smaller than 5% of the mass of the vibrative member, the vibration-damping device possibly suffers from difficulty in exhibiting a desired damping effect, and if the mass of the pillar-shaped mass member is larger than 15% of the mass of the vibrative member, the vibration-damping device suffers from a problem of increase in the overall weight of the device. In the case where a plurality of vibration-damping devices are mounted on the vibrative member, or a plurality of mass members are housed in the housing member, the total mass of the plurality of pillar-shaped mass members is desirably arranged to be held within a range of 5-15% of the mass of the vibrative member.